Boiler displays error 11, domestic hot water does not start when tap is opened, heating may still work.

Safety: Isolate power and close the cold water inlet before working on DHW components. Water may be hot; use caution.

• Check tap flow: Ensure there is adequate cold water flow at the hot taps. If flow is very low, clean inlet filters and check stop valves.
• Inspect DHW flow sensor: Locate the DHW flow sensor on the cold inlet to the boiler. Remove and check for debris or scale. Clean the sensor and its filter screen. Replace if the sensor body is cracked or the turbine does not spin freely.
• Check diverter valve movement: During a hot water demand, observe whether the diverter motor moves. If it does not, the valve may be stuck or the motor faulty. Free the valve or replace the diverter assembly as needed.
• Verify wiring: Ensure the DHW sensor connector is firmly attached to the PCB and that the cable is not damaged.
• Test operation: Restore water and power, open a hot tap, and confirm that the boiler recognises flow and fires without showing error 11.